This invention relate to a metal golf head club having a hollow shell cast of metal.
Recently, in view of the stability of quality, the ease of supply of materials and so on, there have extensively been used metal golf club heads (hereinafter referred to as "head") having a shell cast of metal, such as stainless steel, a titanium alloy and an aluminum alloy, instead of natural wood such as persimmon and cherry.
FIG. 8 shows a metal head of this type disclosed in U.S. Pat. No. 5,056,705. This head 1 comprises a shell 3 of a titanium alloy fully open at its lower end, and a sole plate 5 of pure titanium welded to the shell 3 to close this low end opening. A weight-adjusting member (weight) 7, lowering the center of gravity of the head 1, is affixed to an inner surface of the sole plate 5.
FIG. 9 shows a metal head disclosed in Japanese Pat. Examined Publication No. 53-40380, and this head 9 also comprises a shell 11 of an aluminum alloy fully open at its lower end as shown in FIG. 10, and a sole plate 13 of an aluminum alloy fixedly secured by screws to the lower end of the shell 11 to close this lower end opening as shown in FIGS. 9 and 11. Although not shown in the drawings, a weight-adjusting member is affixed to an inner surface of the sole plate 13.
FIG. 12 shows a metal head disclosed in U.S. Pat. No. 5,195,747, and this head 15 comprises a hollow shell 17 cast of metal, and a sole plate 19 of metal fixedly secured to a bottom surface (sole portion) of the shell 17. A weight-adjusting member 23 is provided in a filler 21 filled in the shell 17.
However, in the head 1 of FIG. 8, the sole plate 5 is secured to the shell 3 to close the lower end opening in this shell, and thus serves much as a lid, and a welding surface is provided only at the peripheral edge of the opening in the shell 3. Therefore, when that portion 5a of the peripheral surface of the sole plate 5 disposed at the face side bites into the ground 27 at the time of hitting a ball 25 as shown in FIG. 13, the sole plate 5 may be disengaged from the shell 3 because of its impact.
Such a disadvantage may also be encountered with the head 9 of FIG. 9, and when the screws 29, securing the sole plate 13 to the shell, become loosened, there is a possibility that the sole plate 13 may be disengaged from the shell 11 because of an impact produced when the sole plate bites into the ground at the time of hitting a ball. Similarly, in the head 15 of FIG. 12, there is a possibility that the sole plate 19 may be disengaged from the shell 17.
In each of the above conventional constructions, the weight-adjusting member is provided in the head to lower the center of gravity of the head. There has been made a proposal in which instead of providing such a weight-adjusting member, a sole plate is cast of metal greater in specific gravity than a shell, and is secured to the shell as is the case with the above sole plates 5 and 19, thereby adjusting the weight of the head.
Even with this construction, however, when that portion of the peripheral surface of the sole plate disposed at the face side bites into the ground at the time of hitting the ball, there is a fear that the sole plate may be disengaged from the shell because of its impact. Thus, it has been difficult to secure the sole plate of metal, which is different from that of the shell and hence provides a rather poor bonding property, to the lower surface of the shell.